1. Field of the Invention
The present invention relates to lighting and more specifically to lighting comprising a transparent medium that exhibits a colored fluorescence when exposed to light.
2. Description of the Related Art
Stores, service centers, and various other business locales routinely employ bright colored signage for decorative and promotional purposes, as well as simply to impart basic information to their patrons. One common example is the neon xe2x80x9copenxe2x80x9d sign. Lettered signs as well as individual letters and logos are ubiquitous in commercial establishments. Bandlights produce long glowing strips of light that are often installed at the top of a building, but are also used to accent the borders of window displays, to draw attention to merchandise therein. Noble-gas and mercury-vapor lamps, commonly known as fluorescent lights, are widespread, because they provide a flexible and low-cost medium for installation within signage and bandlights.
During daylight hours, however, effective design of colored bandlights with eye-catching brightness levels poses an especially difficult problem. Disadvantageously, the luminosity offered by conventional bandlights is insufficient to produce high brightness in daylight. Ambient sunlight, which is about 10,000-foot-candle (lumens per square foot), causes object luminance (being equal to reflectivity times illuminance, expressed in foot-Lamberts) to be in the range of 500 ft-L (black objects) to 8,000 ft-L (white objects). As a result, conventional bandlights are only useful during the nighttime, when their hundreds of foot-Lamberts are very eye-catching. During daylight hours, however, they would preferably be hundreds of times brighter, not a feasible option with electrically powered devices.
Using fluorescent bandlights during the day is not only ineffective, but costly as well as electrical power must be continuously supplied to generate light. It is desirable therefore to have a light-source that will produce adequate brightness and contrast for use during daylight hours, and will not consume large amounts of power.
In one aspect of the invention, a lighting apparatus comprises a collector plate and an elongated lens. The collector plate comprises fluorescent material that radiates fluorescent emission when pumped with light having a wavelength longer than that of the fluorescent emission. The plate comprises opposed surfaces oriented to provide a waveguide that permits at least a portion of the fluorescent emission to propagate towards edges of the plate. The elongated beam-shaping optical element extends along at least one edge of the collector plate and is mounted to receive the fluorescent emission propagating in the collector plate. Preferably, the elongated beam-shaping optical element is in optical contact with the edge of the collector plate and more preferably is indexed matched thereto thereby reducing reflection losses.
In another aspect of the invention, a lighting apparatus includes a collector plate comprising fluorescent material which radiates fluorescent emission when pumped with light having a wavelength shorter than that of the fluorescent emission. The collector plate has opposed surfaces oriented to provide a waveguide that permits at least a portion of the fluorescent emission to propagate towards edges of the plate. The lighting apparatus further comprises reflective material on at least one of the edges of the collector plate to confine light therein. An elongated beam-shaping optical element extends along at least another edge of the collector plate and is mounted to receive the fluorescent emission propagating in the collector plate.
In yet another aspect of the invention, a lighting apparatus comprises a collector plate and an elongated non-imaging optical element. The collector plate comprising fluorescent material which radiates fluorescent emission when pumped with light having a wavelength shorter than that of the fluorescent emission. The plate has opposed surfaces oriented to provide a waveguide that permits at least a portion of the fluorescent emission to propagate towards edges of the plate. The elongated non-imaging optical element extends along at least one edge of the collector plate and is mounted to receive the fluorescent emission propagating in the collector plate.
In still another aspect of the invention, a lighting apparatus comprises a substantially planar collector plate and an asymmetric optical element. The collector plate comprises fluorescent material which radiates fluorescent emission when pumped with light having a wavelength shorter than that of the fluorescent emission. The plate also includes opposed surfaces oriented to provide a waveguide that permits at least a portion of the fluorescent emission to propagate through the collector plate towards an edge of the plate. The asymmetric optical element extends along the edge of the collector plate and is mounted to receive the fluorescent emission propagating in the collector plate. The asymmetric optical element is configured such that fluorescent emission is output from the asymmetric optical element asymmetrically with respect to the collector plate.
In yet another aspect of the invention, a lighting apparatus comprises a collector plate, an elongated optical element, and one or more of light sources. The collector plate comprises fluorescent material which radiates fluorescent emission when pumped with light having a wavelength shorter than that of the fluorescent emission. The collector plate also includes opposed surfaces oriented to provide a waveguide that permits at least a portion of the fluorescent emission to propagate towards edges of the collector plate. The elongated optical element extends along at least one edge of the collector plate and is mounted to receive the fluorescent emission propagating in the collector plate. The one or more light sources are disposed adjacent one edge of the collector plate to introduce light therein.
In still another aspect of the invention, a method of providing decorative illumination comprising providing a fluorescent plate on a real property structure; the fluorescent plate comprises fluorescent material that emits fluorescent light when exposed to sunlight. The real property structures are selected from the group consisting of a building, a tower, a pavilion, a canopy, an archway, a column, a post, a wall, a divider, a fence, a statue, a sculpture, a sign, and a billboard. The fluorescent plate is exposed to sunlight such that the fluorescent material emits fluorescent light. At least a substantial portion of the fluorescent light is guided within the fluorescent plate for emission from an edge thereof and emission emission of light from the edge is altered utilizing an optical element juxtaposed adjacent the edge.
In another aspect of the invention, a lighting apparatus comprises a substantially optically transmissive medium that exhibits a colored fluorescence when exposed to light. This fluorescing medium is extended in the configuration of a planar slab, which acts as a waveguide trapping a majority of the fluorescent emission via total internal reflection. One planar face receives the excitation light, preferably sunlight when the slab oriented, e.g., horizontally. The shorter wavelengths of the sunlight cause the slab""s medium to fluoresce, which gives the faces of the slab a colored appearance. The luminance of most of the slab, however, is insufficient for it to elicit a strong glowing appearance due to the surrounding scene being brightly daylight. The exception is the edge of the slab. Accumulation of the waveguided light, propagating horizontally down the planar slab, results in the edge of the slab displaying a much higher brightness (5-15 times brighter) than the rest of the slab. This enhanced side-emission gives the edge of the slab an eye-catching, visually compelling glow, which is visible from virtually all directions. An optical element can be used to magnify the thickness of the slab edge, consequently reducing the solid angle within which this enhanced glow is visible, as dictated by the optical principle of the conservation of etendue (surface area multiplied by field-of-view). The pattern of emission created corresponds to a continuous elongated strip of light, similar to that produced by neon bulbs. Such a glowing edge, for example, mounted on the top of a building as a daytime bandlight, can have its emission directed downwards toward the ground, not wastefully upwards toward the sky so as to provide eye-catching signage or decoration on a building without needing to supply electrical power during daytime operation.